Insoluble contaminants may appear as haze, precipitates or sediments in biodiesel produced from various feedstock of vegetable and animal origin. This may prevent the product from complying with the requirements on contamination and filterability according to the biodiesel quality standards e.g. in Europe (EN 14214), US (ASTM D6751) and Germany (DIN 51606). The appearance of haze, precipitates or sediments have been found amongst other parameters to be linked to the presence of free steryl glycosides as described in Van Hoed, V. et al. “Identification and occurrence of steryl glucosides in palm and soy biodiesel.” J Am Oil Chem Soc (2008) vol. 85: p. 701-709; Moreau, R A. et al. “The identification and quantification of steryl glucosides in precipitates from commercial biodiesel.” J Am Oil Chem Soc (2008) vol. 85: p. 761-770; and Tang, H. et al. “Fuel properties and precipitate formation at low temperature in soy-, cottonseed-, and poultry fat-based biodiesel blends.” Fuel 87 (2008) 3006-3017.
Accordingly, removal of steryl glycosides from biodiesel is therefore often necessary and a few methods based on filtering or adsorption have been described in WO 2007/076163 which describes a process for treating biodiesel comprising placing biodiesel in contact with a compound capable of removing steryl glycosides from the biodiesel by adsorption; US 2007/0175091 which describes a method for removing impurities from biodiesel comprising: (a) converting a feedstock into biodiesel having a temperature exceeding 98° C.; (b) cooling the biodiesel to a temperature range sufficient to form particulates of impurities; and (c) filtering the cooled biodiesel to remove the particulates; and WO 2008/051984 which describes a method of passing a biodiesel stream through a filter having a molecular weight cut-off of less than 1,000,000 g/mol.
However, these methods of physically removing steryl glycosides are associated with a yield loss of biodiesel. Hence, there is still a need for alternative processes to remove steryl glycosides from biodiesel with low yield-loss, to provide products that are able to meet the biodiesel quality standards on contamination and filterability and which do not suffer from fuel filter plugging problems.
JP08070885A (Nisshin Oil Mills Ltd.) (Database WPI/Thomson AN 1996-203163) discloses a method of manufacturing an acylated steryl glycoside for use in health foods, drugs, agrochemicals and cosmetics which comprises reacting the steryl glycoside with a fatty acid in an aqueous solution containing a lower alcohol or chloroform in the presence of a lipase.